Apparatus and method for controlling ranging of mobile terminals in wireless communication system

ABSTRACT

Disclosed are an apparatus and a method for controlling ranging in a wireless communication system. The apparatus according to the present invention comprises a Radio Frequency (RF) module converting RF band signals received via antenna to low-frequency band signal; a Fast Fourier transform (FFT) module converting the low-frequency band signal of time-domain to frequency-domain signal; a derandomizer performing derandomizing the frequency-domain signals by using a random sequence being transmitted by the terminals; a depermutation module combining the frequency-domain signals output from the derandomizer by unit of burst and outputting the combined signal; and a ranging controller controlling periodic ranging of the terminal corresponding to the respective bursts by estimating phase change in the frequency-domain signals of burst unit.

TECHNICAL FIELD

The present invention relates to an apparatus and a method for controlling a ranging of mobile terminals in a wireless communication system, and more particularly to an apparatus and a method for controlling the ranging of mobile terminals by a base station in case periodic ranging is not performed by the terminal.

BACKGROUND ART

An Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system performs communication through ranging between a terminal and a base station, considering mobility of the terminal, whereas an IEEE 802.16a communication system does not consider mobility of a subscriber.

The ranging can be classified into an initial ranging, a bandwidth request ranging, and a periodic ranging according to the purpose. The initial ranging is performed to obtain synchronization between the base station and the terminal. More specifically, the initial ranging sets correct time and frequency offset between the base station and the terminal, and adjusts transmission power. The periodic ranging is periodically performed by the terminal in which the time offset and the transmission power is set through the initial ranging with respect to the base station, in order to readjust the time offset and the transmission power according to the channel state. The bandwidth request ranging is performed to request allocation of the bandwidth so that the terminal set in the time offset and the transmission power can perform actual communication with the base station.

When the terminal has no data to be transmitted on the uplink channel for a while, the periodic ranging is determined and performed.

However, when data is being continuously transmitted on the uplink channel, the terminal does not perform the periodic ranging. When such a state is continued and furthermore the terminal approaches the base station from a distance, transmission delay is reduced and the data is received to the base station faster than expected. In this case, a signal distortion may be incurred.

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an apparatus and a method for controlling ranging that adjusts transmission timing of uplink signals in a wireless communication system.

It is another object of the present invention to provide an apparatus and a method for controlling ranging that adjusts transmission timing of an uplink signals in a communication system supporting Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiplexing Access (OFDM/OFDMA).

It is yet another object of the present invention to provide an apparatus and a method for controlling ranging that adjusts transmission timing of an uplink signal in a communication system supporting Institute of Electrical and Electronics Engineers (IEEE) 802.16d/e standard.

It is yet another object of the present invention to provide an apparatus and a method for controlling ranging transmission time of an uplink in a communication system supporting Wireless Broadband Internet/Worldwide Interoperability for Microwave Access (WiBro/WiMAX).

It is yet another object of the present invention to provide an apparatus and a method for controlling periodic ranging.

It is yet another object of the present invention to provide an apparatus and a method for controlling initiation of the periodic ranging in a wireless communication system.

It is yet another object of the present invention to provide an apparatus and a method for controlling ranging that adjusts transmission timing of an uplink signal by estimating phase change in a wireless communication system.

Technical Solution

According to an aspect of the present invention, there is provided an apparatus for controlling ranging of a terminal in a wireless communication system, comprising a Radio Frequency (RF) module for converting RF band signal received via antenna to low-frequency band signal; a Fast Fourier Transform (FFT) module for converting the time-domain low-frequency band signal to a frequency-domain signal; a derandomizer for offsetting a random number included in the signal being transmitted by the terminal, with respect to the frequency-domain signal; a depermutation module for combining the frequency-domain signal output from the derandomizer by unit of burst and outputting the combined signals; and a ranging controller for controlling periodic ranging of the terminals corresponding to the respective bursts by estimating phase change in the frequency-domain signal of burst unit.

The ranging controller controls the periodic ranging of the terminal corresponding to the burst, by estimating phase change of pilots included in the frequency-domain signal of burst unit, by unit of burst, averaging the estimated phase changes, and comparing the average phase change with a threshold value for determining the periodic ranging of the terminal.

A method for controlling ranging of a terminal in a wireless communication system, according to the present invention, comprises steps of receiving signal from a plurality of terminals and converting the received RF band signal to low-frequency band signal; converting the time-domain signal of the low frequency band to frequency-domain signal; offsetting a random number included in signal being transmitted by the terminal, with respect to the frequency-domain signal; combining the frequency-domain signal in which the random number is offset, by unit of burst; and controlling periodic ranging of the terminal corresponding to the respective burst by estimating phase change in the frequency-domain signals of burst unit.

The controlling step comprises steps of estimating the phase change of pilots included in the frequency-domain signal of burst unit; averaging the estimated phase change; and controlling periodic ranging of the terminal corresponding to the burst by comparing the average phase change with a threshold value for determining the periodic ranging.

Advantageous Effects

According to the present invention, a time delay of the signal can be predicted in a base station by estimating phase change using the signal received from a terminal. Since periodic ranging of the terminal is controlled using the predicted delay, transmission timing of the terminal can be adjusted.

Since the periodic ranging of the terminal is controlled by the base station, signal distortion due to the time delay can be prevented.

In a communication system supporting Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiplexing Access (OFDM/OFDMA), the transmission timing of the uplink signal is adjusted by predicting the time delay of the signal based on the phase change of pilots and controlling the periodic ranging.

Also, in a communication system supporting Institute of Electrical and Electronics Engineers (IEEE) 802.16d/e standard, the transmission timing of the uplink signal is adjusted by predicting the time delay of the signal based on the phase change of pilots and controlling the periodic ranging. Accordingly, the signal distortion can be prevented.

In addition, in a communication system supporting Wireless Broadband Internet/Worldwide Interoperability for Microwave Access (Wibro/WiMAX), the transmission timing of the uplink signals is adjusted by predicting the time delay of the signal based on the phase change of pilots and controlling the periodic ranging. Accordingly, the signal distortion can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a view showing the structure of a base station in a wireless communication system, according to an embodiment of the present invention;

FIG. 2 is a view showing the structure of a periodic ranging controlling apparatus of a terminal according to an embodiment of the present invention;

FIG. 3 is a view showing the structure of a transmission signal when the communication system uses a Partial Usage of Sub-Channels (PUSC) mode for an uplink channel;

FIG. 4 is a detailed view of a tile of the transmission signal when the communication system uses the PUSC mode for an uplink channel; and

FIG. 5 is a flowchart illustrating a method for controlling periodic ranging of the terminal according to an embodiment of the present invention.

MODE FOR THE INVENTION

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Well known functions and constructions are not described in detail since they would obscure the invention in unnecessary detail.

In a wireless communication system applying the present invention, a terminal being allocated with an uplink channel transmits data to a base station. Then, the base station receives signals of burst unit transmitted from a plurality of terminals.

Referring to FIG. 1, the base station comprises a Radio Frequency (RF) module 110, a Fast Fourier Transform (FFT) module 120, a derandomizer 130, a depermutation module 140, ranging controller 150 and a scheduler 160. The ranging controller 150, in connection with the output of the depermutation module 140, controls the ranging operation of the terminal using an output signal from the depermutation module 140. The scheduler 160 is connected to the ranging controller 150, and instructs the terminal to initiate the periodic ranging by transmitting a Ranging Responding (RNG-RSP) message to the base station, based on the ranging control signal from the ranging controller 150.

The RF module 110 converts an RF band signal received via antenna to a low-frequency band signal. The FFT module 120 converts a low-frequency band signal of time-domain to a frequency-domain signal. The derandomizer 130 offsets a random number included the signal being transmitted by a transmitter, by multiplying the same random number by the frequency-domain signal converted by the FFT module 120. The depermutation module 140 depermutates to collect, by the burst, the signal transmitted on the respectively different sub-carriers. The signal collected by the burst is input to the ranging controller 150.

Hereinafter, the ranging controller 150 that controls the ranging of the terminal, being included in the base station of the wireless communication system, will be described in greater detail according to an embodiment of the present invention.

The ranging controller 150 receives signals from a plurality of terminals, estimates phase change of pilots included in the signals transmitted from a certain terminal by unit of burst, removes noise by averaging the estimated phase changes, and compares the average phase change with a threshold value, thereby controlling the ranging of the terminal.

Referring to FIG. 2, in detail, the ranging controller 150 comprises a phase change estimation unit 210, an average unit 220, and a determination unit 230.

The phase change estimation unit 210 estimates the phase change with respect to all the terminals. To be more specific, the ranging controller 150 controls the ranging of each terminal by estimating the phase change with the signal of each terminal. Since the ranging control for the respective terminals is performed in the same manner, the method of ranging control will be described in regard to any one terminal among the plurality of terminals.

The phase change estimation unit 210 estimates the phase change using the pilots included in the signal being output from the depermutation module 140 by unit of burst. The phase is changed in the frequency-domain signal when time delay of the signals received by the base station occurs. In case 10 samples of time delay occur in the received signal, for example, the phase change is generated in consecutive sub-carriers as expressed by [Equation 1] as follows:

θ=2×π×10/1024  [Equation 1]

wherein, 1024, which is a variable value, refers to the number of the sub-carriers transmitting the signals.

In addition, for example, when the Partial Usage of Sub-Channels (PUSC) mode is used on the uplink channel of the communication system, each burst includes a plurality of sub-channels, each sub-channel includes 6 tiles, each tile includes 4 pilots, and the pilots are distanced by 3 sub-carriers respectively in the same symbol. Thus, the phase change can be expressed by [Equation 2] as follows:

θ=2×π×10×3/1024  [Equation 2]

When the communication system applies the PUSC mode of the uplink channel, the transmission signal is structured as shown in FIG. 3. More specifically, each channel includes 6 tiles, and each tile includes 4 pilots. To illustrate the respective tiles in greater detail, FIG. 4 shows the structure of tile ‘i’.

Tile ‘i’ comprises 4 pilots, that is, P_(i,1), P_(i,2), P_(i,3), and P_(i,4). Two pilots in one OFDMA symbol are distanced by 3 sub-carriers from each other.

In this case, the phase change estimation unit 210 performs the estimation of phase change by [Equation 3] as follows:

$\begin{matrix} {\theta = {\frac{1}{3}{\arctan \left( {\sum\limits_{k = 0}^{K - 1}{\sum\limits_{i = 0}^{5}\left( {{P_{k,i,1} \times P_{k,i,3}^{*}} + {P_{k,i,2} \times P_{k,i,4}^{*}}} \right)}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack \end{matrix}$

wherein, ‘k’ refers to the index of sub-channels included in one burst, ‘K’ refers to the number of sub-channels included in one burst, and ‘i’ refers to the index of tiles included in one sub-channel. Here, one sub-channel includes 6 tiles.

When the phase change is estimated and output by unit of burst by the phase change estimation unit 210, the average unit 220 averages the estimated phase changes because the output value may not be accurate when the received signal includes much noise. Therefore, the average unit 220 averages the phase changes to remove the noise, using [Equation 4] as follows:

θ_(avg)=(1−α)θ_(avg)+αθ  [Equation 4]

wherein, θ_(avg) refers to the average of the phase changes, and ‘α’ refers to an average coefficient.

When the average unit 220 outputs the average phase change θ_(avg), the determination unit 230 controls the ranging of the terminal by comparing the average phase change θ_(avg) to a predetermined threshold value θ_(th). The threshold value θ_(th) is a reference value for determining whether the periodic ranging of the terminal is required for the reception delay.

More particularly, when the average phase change θ_(avg) is smaller than the pre-determined threshold value θ_(th), the determination unit 230 controls the terminal to initiate the periodic ranging.

Additionally, the determination unit 230 initializes the average phase change θ_(avg) to a value greater than the threshold value θ_(th). Although the periodic ranging is initiated by the terminal, the determination unit 230 performs such initialization FIG. 5 illustrates a method for the base station to control the ranging of the terminal in the wireless communication system, according to the embodiment of the present invention.

In FIG. 5, the phase change is estimated by unit of burst with respect to the signal including pilots (S510). Since the estimation of phase change is performed as already described regarding the phase change estimation unit 210, detailed description thereof will be omitted.

When the phase change is estimated by unit of burst, the average of the phase changes for the respective bursts is obtained to thereby remove the noise included in the signal (S520).

When the average phase change is smaller than the predetermined threshold value (S530), the terminal is controlled to initiate the periodic ranging with respect to the corresponding burst (S540). Here, the threshold value is the reference for determining whether performing the periodic ranging due to the time delay of the signals received by the base station.

While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims. 

1-20. (canceled)
 21. A method for controlling transmission timing of an uplink in a wireless communication system, the method comprising: receiving from at least one terminal a pilot signal, wherein the pilot signal is generated by a predefined equation based on a phase shift; and transmitting a response message which indicates a timing offset for uplink transmission in response to the pilot signal.
 22. The method of claim 21, wherein the response message is used for indicating an uplink scheduling.
 23. The method of claim 22, wherein the uplink scheduling is performed based on the phase shift.
 24. The method of claim 21, wherein the pilot signal is received by predefined units of burst.
 25. The method of claim 21, wherein the timing offset is the change of the uplink timing relative to the current uplink timing.
 26. A method for controlling transmission timing of an uplink in a wireless communication system, the method comprising: transmitting a pilot signal to a base station (BS), wherein the pilot signal is generated by a predefined equation based on a phase shift; receiving from the BS a response message which indicates a timing offset for uplink transmission in response to the pilot signal; and adjusting the transmission timing of the uplink based on the timing offset.
 27. The method of claim 26, wherein the response message is used for indicating an uplink scheduling.
 28. The method of claim 27, wherein the uplink scheduling is performed at the BS based on the phase shift.
 29. The method of claim 26, wherein the pilot signal is transmitted by predefined units of burst.
 30. The method of claim 26, wherein the timing offset is the change of the uplink timing relative to the current uplink timing.
 31. A method for controlling transmission timing of an uplink in a wireless communication system, the method comprising: receiving a pilot signal from at least one terminal; estimating a phase shift by using the received pilot signal; and transmitting a response message based on the estimated phase shift for uplink timing adjustment.
 32. The method of claim 31, wherein the response message is used for indicating an uplink scheduling.
 33. The method of claim 32, wherein the uplink scheduling is performed based on the phase shift.
 34. The method of claim 31, wherein the signal is transmitted by predefined units of burst.
 35. A method for controlling transmission timing of an uplink in a wireless communication system, the method comprising: receiving a pilot signal from at least one terminal, wherein the pilot signal is generated by a predefined equation based on a phase shift; estimating a timing offset for uplink transmission based on the received pilot signal; and transmitting a response message which indicates the timing offset in response to the pilot signal.
 36. The method of claim 35, wherein the response message is used for indicating an uplink scheduling.
 37. The method of claim 36, wherein the uplink scheduling is performed based on the phase shift.
 38. The method of claim 35, wherein the pilot signal is received by predefined units of burst.
 39. A terminal for controlling transmission timing of an uplink in a wireless communication system, wherein the terminal is configured to transmit to a base station (BS) a pilot signal which is generated by a predefined equation based on a phase shift, receive from the BS a response message which indicates a timing offset for uplink transmission in response to the pilot signal, and adjust the transmission timing of the uplink based on the timing offset.
 40. The terminal of claim 39, wherein the response message is used for indicating an uplink scheduling.
 41. The terminal of claim 40, wherein the uplink scheduling is performed at the BS based on the phase shift.
 42. The terminal of claim 39, wherein the terminal transmits the pilot signal by predefined units of burst.
 43. The terminal of claim 39, wherein the timing offset is the change of the uplink timing relative to the current uplink timing. 